From AMS Glossary
(Abbreviation for intermediate frequency signal.) The signal at an intermediate stage of radar and lidar receivers, chosen at a standard frequency (often 30 or 60 MHz) where amplifiers and filters are commonly available.
The radar or lidar echoes are converted to IF signals by a mixer, which shifts the frequency of the signals through the use of a local oscillator. Information is extracted from IF signals by detection or coherent detection.